This invention relates to ground water pollution control, in particularly to the recovery of liquid pollutants which are substantially immiscible with water and tend to rest above the water table in a water-bearing ground formation.
An effective way for extracting a liquid hydrocarbon or other water-immiscible pollutant from ground water is to drill a well in the center of the contaminated region to a depth well below the water table, then lower the water level in the well by pumping out water, and finally remove pollutant from the layer floating above the water in the well as the pollutant flows inward from the surrounding area by gravitational flow. Pollutant removal is generally achieved by a pump which is designed or programmed to draw liquid from the pollutant layer only. Extraction is generally begun while the pollutant is still a plume in the ground formation above the water table, before extensive lateral spreading over the water table due to gravitational force has occurred. Several strategically placed wells are often required, depending on the size of the plume, the degree of spreading, and the shape of the contaminated area. The depth to which the water level in any particular well must be lowered will depend on the size of the plume.
Typical of existing devices is that disclosed in Solomon, U.S. Pat. No. 4,273,650 (June 16, 1981), wherein an electric pump for periodic operation is lowered directly into the well and submerged in the hydrocarbon layer above the water table. By placing an electric motor in direct contact with a frequently flammable pollutant, this device poses a serious risk of fire or explosion. In addition, soil, rock and other debris present in the well interfere with the pump, resulting in frequent malfunctions and clogging of lines.